This invention relates to a circuit arrangement suitable for igniting a high-pressure discharge lamp. The circuit arrangement is provided with transformer means, switching means and capacitive means for periodic charge change via the transformer means and switching means, and also provided with peak current limiting means to protect the switching means. The invention also relates to a lamp operating circuit provided with such a circuit arrangement.
A circuit arrangement of the kind mentioned in the opening paragraph is known from DE-OS 33 39 814. The peak current limiting means there takes the form of a coil. Another possibility is to use a resistor as the peak current limiting means. Combinations of the said means are also possible.
The known circuit arrangement is very suitable for igniting high-pressure discharge lamps, such as metal halide lamps and high-pressure sodium lamps. A primary part of the transformer means is then included in an electric circuit which comprises both the capacitive means and the switching means. A voltage pulse generated in this circuit as a result of the switching means becoming conductive and the ensuing charge change of the capacitive means is transformed in the transformer means into a high voltage pulse at a secondary part, to which the lamp to be ignited is connected.
Although the peak current limiting means influence the level of an ignition pulse generated in the transformer means, this pulse level will be to a considerable degree dependent on the load on the transformer means. The transformer load is made up of the connected lamp including the connection lines.
In particular, the impedance formed by the connection lines is of major importance. The application possibilities of the known circuit arrangement are limited by this. Thus, if the circuit arrangement is dimensioned so as to ignite a lamp with comparatively long connection lines, so a comparatively great impedance, this circuit arrangement will not be suitable for igniting a similar lamp with comparatively short connection lines, since the ignition pulses will then become considerably higher than can be safely allowed. Conversely, a circuit arrangement dimensioned so as to ignite a lamp via comparatively short connection lines will generate ignition pulses which are insufficiently high for igniting a similar lamp with the use of comparatively long connection lines.